The rapid increase in cesarean delivery in the United States since 1970 has signalled the need for an in-depth assessment of this technology and its current application. The proposed study uses a hospital-based case-control design to understand the factors related to the outcome of surgical birth. Phase I of the project is designed to determine the extent to which the need for a primary cesarean delivery is based on information detectable before labor begins versus information known only after the onset of labor. Phase II examines diptoria (difficult labor) as it relates to the use of cesarean section. A logistical regression analysis will be carried out in order to assess the way in which characteristics of physicians (time of training, speciality, type of practice) and patients (mode of payment), modify the probability that a woman with prolonged labor will have a surgical birth. Cases and controls will be selected from two existing computerized perinatal data bases: the Regional Perinatal Project data base at Los Angeles County/Harbor/UCLA Medical Center, and the Cedars-Sinai detailed antepartum, intrapartum and newborn outcome data, and will be linked with information about the delivering physicians.